Connecting a circuit-switched wireless access network to an IP multimedia subsystem

ABSTRACT

A network device performs a delayed registration in connection with phone call setup, if the network device does not know a phone number of a user in question at the time of updating the location updating. In addition, the network device performs user authentication and creates and maintains an encrypted and secure network connection between the network device and an IP multimedia subsystem by using data security mechanisms of a terminal of the IP multimedia subsystem and the authentication and data security parameters of the terminal received from the IP multimedia subsystem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/FI2007/050027 International Filing Date, 18 Jan. 2007, whichdesignated the United States of America, and which InternationalApplication was published under PCT Article 21 (s) as WO PublicationWO2007/085692 A1 and which claims priority from, and the benefit of,Finish Application No. 20060046 filed on 19 Jan. 2006, the disclosuresof which are incorporated herein by reference in their entireties.

The aspects of the disclosed embodiments relate to a system and a methodfor connecting a wireless radio access network directly to an IPMultimedia Subsystem (IMS) specified by 3GPP (the 3^(rd) GenerationPartnership Project) with a multi-radio protocol gateway (MRGW)according to the disclosed embodiments.

BACKGROUND

As the wireless access network it is possible to use radio networks ofpublic mobile phone systems, such as, for example, GSM, IS-54, IS-95,CDMA-2000 and WCDMA radio networks, as well as radio networks usingunlicensed radio frequencies, such as, for example, a wireless localarea network in its different forms (for example different versions ofIEEE 802.11) and Bluetooth networks. The access networks can be used inboth a circuit-switched mode (radio networks of public mobile phonesystems) and a packet-switched mode (radio networks using unlicensedradio frequencies) for circuit-switched services (reference: UMA). UMA(Unlicensed Mobile Access) refers to a manner specified by the UMAconsortium for relaying the circuit-switched signaling protocols of apublic mobile phone system over a TCP/IP connection by utilizing, forexample, any unlicensed radio frequency. The IP multimedia subsystem isa public mobile core network specified by 3GPP, with which multimediaservices are produced to end users with wireless terminals compatiblewith the IP multimedia subsystem. The services of the IP multimediasubsystem are based on combinations of sound, images, data and text andthey are used over a packet-switched transmission path and connection.

A central service of the IP multimedia subsystem will be an IP telephoneservice, which will implement, and possibly in the future also replace,conventional circuit-switched telephone services (i.e. teleservices) aswell as supplementary services connected to them (i.e. call transfer,call holding/call pickup, etc.) in public mobile phone networks.However, a General Packet Radio Service (GPRS) in public mobile phonenetworks is not necessarily the best possible or the most cost-effectiveway to relay information requiring real-time, such a audio and video,over a wireless access network. In a core network a packet-switchedtransfer method based on data network protocols of prior art is a usefuland cost-effective way to relay information requiring real-time, but fora wireless access network this is not the case, not necessarily even inaccess networks using unlicensed radio frequencies, when large numbersof users are involved. The packed-switched transfer method in wirelessaccess networks of public mobile phone systems is designed especiallyfor transferring narrow-band audio and video and it is the only audio ina wireless manner when large numbers of users are involved. This issueis discussed in 3GPP as well, where specification work for roamingpacket-switched bearer services and IP multimedia subsystem session hasbeen started.

Publications US 2003/0027569 A1, US 2003/0027595 A1 and US 2003/0026245A1 disclose a system and a new entity (iMSC), by means of which thecircuit-switched services of a public mobile core network can beimplemented in the IP Multimedia Subsystem (IMS) specified by the 3GPP(3^(rd) Generation Partnership Project). The publications disclose a newentity called iMSC, which converts the circuit-switched locationupdating and the voice service and feature control into SIP operationsaccording to an IP multimedia subsystem. The publications do notdirectly describe how the conversion is performed, but they refer toknown operation modes of a public mobile phone network and to the knownoperations of the elements of a public mobile phone system.

For example, the publications disclose that the iMSC performsregistration of the user equipment (UE) in the IP multimedia subsystem,but they do not disclose which public user identity the iMSC registersin the IP multimedia subsystem for the user's terminal nor which addresssaid public user identity is connected to by means of the addressconnection being registered. In accordance with the recommendations ofthe IP multimedia subsystem of 3GPP—to which the publicationsrefer—there may be several registered public user identities and theymay be in the form of a SIP resource identifier (SIP URI, UniformResource Identifier) or a uniform resource locator meant for a telephonenumber.

The above-mentioned public user identities are stored in anIP-multimedia-subsystem-specific subscriber identity module (SIM) card.If no public user identities are specified, one public user identity isderived according to the 3GPP recommendations from the InternationalMobile Subscriber Identity (IMSI) of the user, which is then registeredin the IP multimedia subsystem. IMSI specifies the subscriber connectionunambiguously, but IMSI is not a telephone number with which or to whichit is possible to call from a conventional mobile phone or telephonenetwork, and not necessarily even within the IP multimedia subsystem. Ingeneric IP telephony networks the spectrum of public user identities iseven wider, when proprietary systems, such as Skype, are also taken intoaccount.

If now a mobile phone number is registered in the IP multimediasubsystem as the user's public address and the domain name of the iMSCas the address connection, as a person skilled in the art can assumefrom the operational descriptions of the publications in question and onthe basis of the recommendations of 3GPP and IETF—and which is anabsolute condition for the solution disclosed in the publications toeven function—it still remains unclear how the address connectionregistered for the user is provided to the ENUM/DNS service. It is notspecified in the recommendations of 3GPP or IETF either.

For the part of call control the operation of the conversion isdescribed in FIG. 3 of the publications, where the operation of iMSC isdescribed by two known elements ‘MSC Server’ and ‘P-CSCF’. A personskilled in the art can on the basis of the publications assume thatreference is made to elements specified in the 3GPP recommendations andtheir operation, in which case it remains unclear how the conversion ismade, because neither of the above-mentioned elements supports theconversion of call control signaling in any way as such, and in thepublications in question the way the conversion is made is not specifiedas a new operation for said elements. Elsewhere in the publications itis disclosed that the iMSC behaves like a combination of a SIP UserAgent, (SIP UA) and ‘P-CSCF’. Further, a person skilled in the art canon the basis of the publications assume that reference is made toelements specified in the 3GPP recommendations and their operation, inwhich case it remains unclear how, for example, the conversion of a callcontrol signaling is made, because neither of the above-mentionedelements supports the conversion of call control signaling in any way assuch according to the 3GPP recommendations, and in the publications inquestion the way the conversion is made is not specified as a newoperation for said elements.

For the part of call control signaling a more operative combinationwould be, according to the 3GPP recommendations and imitating thepublications in question, for example a combination of‘MSCServer’-‘T-SGW’-‘MGCF’-‘B-CSCF’ or ‘MSC Server’-‘T-SGW’-‘MGCF’. Thesame applies for the conversion of circuit-switched supplementaryservices. For the part of SIP registration the above-mentionedcombination of the SIP user agent and ‘P-CSCF’ would be more operativefrom the point of view of the SIP connection procedure, if the interfacebetween iMSC and the ‘C-CSCF’ entity mentioned in the publicationswould, in accordance with the 3GPP recommendations, be Gm. The interfacebetween iMSC and the ‘C-CSCF’ entity is now specified by a new interface‘Mx’. In the publications the interface is specified as an interfaceusing the SIP connection procedure according to the procedures of the IPmultimedia subsystem, there are no other specifications for it and inthe 3GPP recommendations the interface in question does not exist. Inaddition, the SIP user agent and ‘P-CSCF’ do not as such support theconversion of the location updating signaling in any way according tothe 3GPP recommendations.

Further, in connection with the location updating of the mobile phonenetwork and registration to the IP multimedia subsystem, FIG. 4 of thepublications shows that the location updating to the mobile phonenetwork is performed first and then the registration to the IPmultimedia subsystem. This may lead to an unfortunate situation for theuser: if the location updating to the mobile phone network is nowsuccessful, but registration to the IP multimedia subsystem fails, theresult is a situation where no calls can be made with the terminal inquestion and no calls are received in it, because the user in questionhas not registered to a core network, i.e. the IP multimedia subsystem.The situation cannot be rectified until the terminal performs a periodiclocation updating or the user switches the terminal off and on again, inwhich case the registration to the IP multimedia subsystem is attemptedagain. In paragraph [0059] of the publication US 2003/0026245 A1, ismentioned the procedure ‘inter-iMSC Location Update’ of the 3GPPrecommendation TS 24.008, which, however, is not specified in therecommendation in question, nor is, for example, the ‘inter-MSC LocationUpdate’ procedure. The same procedure is mentioned in the otherabove-listed publications as well.

The publication mentions the iMSC entity performs the authentication ofthe user, for example paragraphs [0057] and [0059] of US 2003/0026245A1, which on the basis of the description in the publication is anauthentication based specifically on the procedures of a conventionalmobile phone network, i.e. authentication performed by the visitorlocation register VLR on the basis of authentication parameters receivedfrom the home location register HLR over the MAP interface, and not anauthentication performed by an IP multimedia subsystem. This assumptionis also supported by the description of the operation in paragraph[0098] of US 200370026245 A1 (which description of operation can befound in the other publications as well): iMSC entity sends an SIPregistration request to the ‘CSCF’ (first to ‘I-CSCF’, which sends therequest further to ‘S-CSCF’), after which the ‘CSCF’s should performauthentication of the terminal through the iMSC entity by using the SIPauthentication procedure of the IP multimedia subsystem and only thenbring the SIP registration to a finish with ‘HSS’.

SUMMARY

The disclosed embodiments make it possible to combine two cost-effectiveways that have be proven usable in practice for implementing voiceservices in public mobile phone systems, i.e. a circuit-switchedtransmission path in a wireless access network and a packed-switchedtransmission path and service implementation in a service network. Thedisclosed embodiments make it possible for mobile phone serviceproviders to implement an IP multimedia subsystem and to implement voiceservices for those hundreds of millions of users with, for example,ordinary GSM phones. The mobile phone service providers can develop themarket with a new core network technique without them having to investin the additional capacity of a wireless access network and withouthaving to wait for new multifunction terminals to come to the market.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an operational block diagram of an overall system utilizingthe disclosed embodiments;

DETAILED DESCRIPTION

The more specific structure and operation of the overall systemutilizing the disclosed embodiments is described with terms, interfacesand protocols known from GSM and UMTS.

In the overall system according to FIG. 1 a circuit-switched wirelessaccess network (104) of a public mobile phone system is connected to anIP multimedia subsystem (101) via a multi-radio protocol gateway (4)according to the disclosed embodiments. The circuit-switched wirelessaccess network is formed by a base station (1) as well as a basestation/radio network controller (2), which is called a Base StationSubsystem (BSS) in the GSM system and a Radio Network System (RNS) inthe third generation UMTS system. The wireless access network (104) canalso be formed by, for example, an UMA network utilizing unlicensedfrequencies, which network contains wireless radio access points (AP)(30) as well as an UMA network controller (31), or it can be formed of ageneric access network utilizing unlicensed frequencies, which iscomposed of wireless access points (30). A mobile services switchingcenter/visitor location register server (MSC Server) (5), a homelocation register (HLR) (7), an equipment identity register (EIR) (8),service and gateway nodes (SGSN and GGSN) (3) and (10) of a packet radionetwork, as well as an IP multimedia subsystem (101), in turn, form themobile core network. The mobile core network is divided into acircuit-switched part, which comprises the MSC Server (5) (this maynaturally also be a conventional combination of a mobile servicesswitching center and a visitor location register), a packet-switchedpart, which comprises service and gateway nodes (3) and (10) of a packetradio network, a location register part, which comprises the homelocation register (7), the visitor location register (not shownseparately in FIG. 1) and the packet radio network service and gatewaynodes (3) and (10), as well as an IP multimedia subsystem (101), whichincludes a Home Subscriber Server (HSS) (11), a Call Session ControlFunction (CSCF) (9) in its different functional forms (i.e. I-CSCF,P-CSCF, S-CSCF and B-CSCF), an Application Server (AS) (17), a MediaGateway Control Function (MGCF) (14), a Media Gateway (MGW) (15), aswell as a Multimedia Resource Function (MRF) (16). The register gateway(RGW) according to the disclosed embodiments functions as an applicationserver of the IP multimedia subsystem (101).

In the following the interfaces of the multi-radio protocol gatewayaccording to the disclosed embodiments of FIG. 1 will be described morein detail.

When the wireless access network (104) of the public mobile phone systemof FIG. 1 is connected via an interface A (50) or IuCS (71) to amulti-radio protocol gateway (4), the wireless access network (104) seesthe multi-radio protocol gateway (1) and the IP multimedia subsystem(101) behind it as an MSC Server (5) of the public mobile phone system,i.e. as a circuit-switched part of the public mobile core network. Itshould be noted that, for example, the interface (50) can be either areal GSM A interface, or it can be a distributed A interface in such amanner that the lower protocols of the A interface (for example, MTP andSCCP protocols) are implemented with an SS7oIP gateway utilizing theknown ‘SS7 over IP’ gateway technique (not shown in FIG. 1) and theupper protocols of the A interface (for example BSSMAP and DTAPprotocols) in the multi-radio protocol gateway (4), which also supportsthe above-mentioned ‘SS7 over IP’ gateway technique. If the basestation/radio network controller (2) of the wireless access network(104) also supports the above-mentioned ‘SS7 over IP’ gateway technique,said SS7oIP gateway is not needed in the interfaces A (50) and IuCS(71). Said ‘SS7 over IP’ gateway technique is a method specified byIETF, including protocols (i.e. Sigtran protocols), for transferring SS7signaling by utilizing the IP connection protocol. Via the interface Up(52) the terminal (6) sees the multi-radio protocol gateway (4) and theIP multimedia subsystem (101) behind it as an UMA network controller andas an MSC Server (5) of a public mobile phone system, i.e. as acircuit-switched part of the public mobile core network. Via theinterface U (70) the terminal (6) sees the multi-radio protocol gateway(4) and the IP multimedia subsystem (101) behind it as an MSC Server (5)of a public mobile phone system over a TCP/IP (or the like) connectionwhen the terminal (6) performs location updating to a public mobilephone system. It is to be noted that in this case the terminal (6) musthave adequate properties to activate and perform the location updatingprocedure to the mobile phone system over, for example, theabove-mentioned TCP/IP (or the like) connection.

Via the interface Gm (61) of FIG. 1 the session control function (9) ofthe IP multimedia subsystem (101) sees the multi-radio protocol gateway(4) as User Equipment (UE) of the IP multimedia subsystem (101), i.e. asa terminal (6) that is compatible with the IP multimedia subsystem(101), which normally communicates with the session control function (9)of the IP multimedia subsystem via the packed radio network gateway node(10). Via the interface ISC (72) the session control function (9) seesthe register gateway (24) as an application server (17) of the IPmultimedia subsystem (101). Via the interface Sh (73) the homesubscriber server (11) sees the register gateway (24) as an applicationserver (17) of the IP multimedia subsystem (101) as well. Via theinterface Mn (62) the media gateway (15) sees the multi-radio protocolgateway (4) as a media gateway control function (14).

Via the interface D (75) of FIG. 1 the home location register (7) of thepublic mobile phone system sees the register gateway (24) and the IPmultimedia subsystem (101) behind it as the visitor location register ofthe public mobile phone system when the terminal (6) performs locationupdating when transferring from the area of one visitor locationregister to another, or when a call from the public mobile phone systemis relayed to the terminal (6), or when the terminal (6) requests a callrelay to a public mobile phone network, or when subscriber data ischanged and the changed data is transferred between the home locationregister (7) and the register gateway (4) and the IP multimediasubsystem (101) behind it. Via the interface G (76) the MSC Server (5)of the public mobile phone system sees the register gateway (24) and theIP multimedia subsystem (101) behind it as a visitor location registerof a public mobile phone system when the terminal (6) performs locationupdating when transferring from one visitor location register toanother. Via the interface F (77) the equipment identity register (8) ofthe public mobile phone system sees the register gateway (24) and the IPmultimedia subsystem (101) behind it as an MSC Server (5) of the publicmobile phone system when the equipment identity register (8) checks theequipment identity (IMEI) of the terminal (6). Via the interface Ddns(78) the domain name service (DNS) (40) sees the register gateway (24)as a client using the domain name service (40).

The multi-radio protocol gateway (4) according to the disclosedembodiments comprises the following functions. A UNC GW function (18)comprises an UMA radio resource protocol gateway, via which the terminal(6) equipped with UMA properties registers and communicates with themulti-radio protocol gateway (4) and through that with the IP multimediasubsystem (101). The multi-radio protocol gateway (4) does not implementthe actual UMA network controller, but therefore only the UMA radioresource protocol gateway. A SIP GW function (20) comprises a SIPgateway, which implements the functions of the user equipment accordingto SIP specifications of 3GPP, as well as the control of useridentification data and the addresses-of-record of the IP multimediasubsystem (101) and the address bindings connected to sessions. A SGWfunction (22) is the core of the protocol routing function of themulti-radio protocol gateway (4). The SGW function (22) receives andrelays further the location updating, registering, identification,connection, disconnection requests and responses coming from and goingto different interfaces.

The register gateway (24) according to the disclosed embodimentscomprises the following functions. A VLR GW function (19) comprises avisitor location register protocol gateway. A SIP GW function (23)comprises a SIP gateway, which implements the user equipment functionsaccording to the SIP specifications of 3GPP. The functions of thevisitor location register according to the public mobile phone systemcan now be implemented as a combination of SGW (22) and SIP GW (20)functions of the multi-radio protocol gateway, as well as VLR GW (19)and SIP GW (23) functions of the register gateway system (101). A DNS GWfunction (4) comprises the client functions of the domain name service(4) according to IETF specifications extended with the updatingprocedure of the domain name service according to IETF specifications.

In the following, the function of the multi-radio protocol gatewayaccording to the disclosed embodiments in connection with registering tothe IP multimedia subsystem is described more in detail. The descriptionof the function is based on the functions according to the 3GPP and IETFspecifications.

The multi-radio protocol gateway (4) receives the user's internationalmobile subscriber identity from the terminal (6) in the locationupdating request or the multi-radio protocol gateway (4) requests theterminal (6) to send it in an identity message, if the user'sinternational mobile subscribed identity does not come with the locationupdating request. In the To header field of the SIP registration requestthe SIP GW function (20) sets the registration address, which is thepublic user identity of the registering user presented in the form of auniform resource locator (URL) meant for a phone number, which in thiscase is the international mobile phone number (mobile station ISDN,MSISDN) of the above-mentioned registering user, when the multi-radioprotocol gateway (4) knows the international mobile phone number of theuser in question.

If the multi-radio protocol gateway (4) does not know the internationalmobile phone number of the user in question, the SIP GW function (20)immediately sends a location updating response indicating acceptance tothe terminal (6) via the SGW function (22) without performing aregistration to the IP multimedia subsystem (101). In this case theregistration to the IP multimedia subsystem (101) is performed inconnection with the first phone call. In the From header field of theSIP registration request the SIP GW function (20) sets the addressconnection connected to the SIP session services of the user's SIP endpoint, which address connection follows the resource identifierstructure according to the SIP session procedure, including, forexample, the user's international mobile phone number as a characterstring+‘:’ character+‘MSISDN’ character string+‘@’ character+domain nameof the multi-radio protocol gateway (4) or its numeric IP address. Inthe Contact header field of the SIP registration request the SIP GWfunction (20) relays to the IP multimedia subsystem (101) the addressconnection connected to the SIP session services of the user's SIP endpoint, which address connection the SIP GW function (20) also stores inits database (or a corresponding memory).

The above-mentioned address connection of the session services of theSIP end point is the same as the address connection relayed in the Fromheader field, i.e. the user's international mobile phone number as acharacter string+‘:’ character+‘MSISDN’ character string+‘@’character+domain name of the multi-radio protocol gateway (4) or itsnumeric IP address.

In the Username field of the Authorization header field the SIP GWfunction (20) sets the private user identity of the user, which the SIPGW function (20) derives from the user's international mobile subscriberidentity from its country and network codes according to the 3GPPspecifications.

In the Realm field of the Authorization header field the SIP GW function(20) sets an identifier of that network where the user identification isperformed. The network identifier in question is the home networkregistrar's domain name.

In the Request URI field of the Authorization header field the SIP GWfunction (20) sets the request URI of the SIP registration request.

In the Security-Client header field the SIP GW function (20) relays tothe session control function (9) of the IP multimedia subsystem (101)those data security mechanisms, which the terminal (6) supports andwhich are used between the terminal (6) and the session control function(9).

In this case the function differs from the mechanisms specified by 3GPPin that the data security mechanisms in question are used between themulti-radio protocol gateway (4) and the session control function (9) ofthe IP multimedia subsystem (101), and between the terminal (6) and themulti-radio protocol gateway (4) are used the data security mechanismsof a circuit-switched wireless access network of a public mobile phonesystem. The ciphering procedure used between the multi-radio protocolgateway (4) and the session control function (9) is IPsec-3GPP and theintegrity algorithm being used is according to either HMAC-MD5-96 orHMAC-SHA-1-96 3GPP specifications.

In addition to these the multi-radio protocol gateway (4) relays in theother fields of the Security-Client header field the necessaryparameters for creating a secure and encrypted security associationbetween the multi-radio protocol gateway (4) and the IP multimediasubsystem (101), i.e. the Security Parameter Index (SPI) and thecommunication port numbers being used. In addition, the SIP sessionrequest includes a message body for session description, to which theSIP GW function (20) connects the data from the original locationupdating request: the target location area, the identity of the servingcell, the type of the location updating, the International MobileSubscriber Identity (IMSI), the Temporary Mobile Subscriber Identity(TMSI), the previous location area, as well as the Ciphering KeySequence Number (CKSN).

It is to be noted that the data to be connected vary a little dependingon whether the terminal (6) has a second or third generation SIM card.The above-presented data relate to a second generation SIM-card. As thetype of the message body for description is specified an application andas the name of the application, for example, RGW. These are set in theContent-Type header field. The data from the original location updatingrequest is relayed each in their own parameter, for example in thefollowing manner:

OperationCode=location updating,

InvokelD=subscriber identity (i.e. temporary subscriber identity,international subscriber identity or some other identity unambiguouslyidentifying the subscriber),

TargetLocationArealD=target location area,

ServingCellID=identity of the serving cell,

LocationUpdateType=type of the location updating,

IMSI=international mobile subscriber identity,

TMSI=temporary mobile subscriber identity,

PreviousLocationAreald=previous location area, and CKSN=ciphering keysequence number.

After receiving the registration request the session control function(9) of the IP multimedia subsystem (101) starts the authentication ofthe user of the terminal (6) (i.e. the subscriber connection) by sendingan unauthorized response to the multi-radio protocol gateway (4). In theWWW-Authenticate header field of the unauthorized response the sessioncontrol function (9) relays a random number (RAND), an authenticationtoken (AUTN) and the authentication algorithm to be used. In theSecurity-Server header field of the unauthorized response the sessioncontrol function (9) relays the parameters of the ciphering procedureused between the multi-radio protocol gateway (4) and the sessioncontrol function (9), such as the ciphering algorithm being used, thesecurity parameter index and the communication port numbers being used.

After receiving the unauthorized response the SIP GW function (20) sendsa corresponding circuit-switched connection authentication request tothe terminal (6) via the SGW function (22). In the authenticationrequest the SIP GW function (20) relays a random number and anauthentication token to the terminal (6) as well as identifies theauthentication algorithm to be used. After receiving the authenticationrequest the terminal (6) picks the Message Authentication Code (MAC) andthe Sequence Number (SQN) from the authentication token, calculates theExpected MAC, compares it to the authentication code of the receivedmessage and checks that the sequence number is within allowed limits. Ifthe results are positive, the terminal (6) calculates the authenticationchallenge response (RES) and sends the authentication challenge responseto the multi-radio protocol gateway (4) in its authentication requestresponse.

After receiving the authentication request response the SIP GW function(20) stores the user authentication etc. data in a database (or acorresponding memory), creates an Integrity Key (IK) and securityparameter index, as well as a secure and encrypted network connectionand sends a new SIP registration request to the session control function(9) of the IP multimedia subsystem (101) over the secure and encryptednetwork connection, which is formed between the multi-radio protocolgateway (4) and the session control function (9). The SIP GW function(20) adds the private user identity and authentication challengeresponse to the Authorization header field. The content of theSecurity-Client header field is the same as in the first SIPregistration request. The SIP GW function (20) also adds theSecurity-Verify header field to the new SIP registration request inquestion, which contains the contents of the Security-Server headerfield received in the unauthorized response in an unchanged form. Thenew SIP registration request contains the same message body fordescription as the first SIP registration request.

After receiving the second SIP registration request authenticating theuser the session control function (9) finishes the registration with thesubscribers home subscriber server (11) and relays the SIP registrationrequest further to the SIP GW function (23) of the register gateway (24)according to the filter information received from the home subscriberserver (11). After receiving the SIP registration request the SIP GWfunction (23) picks the data of the original location updating requestfrom the request, creates a corresponding location updating request andrelays it to the VLR GW function (19). After receiving the locationupdating request the VLR GW function (19) opens a connection to theprevious visitor location register via the interface G (76) and sendsthe international subscriber identity and the authentication parameterrequest message to the previous visitor location register. The addressof the previous visitor location register is derived from the previouslocation area. In the request message also the temporary subscriberidentity is relayed to the previous visitor location register. Theprevious visitor location register responds to the request by sendingauthentication parameters and the international subscriber identity tothe VLR GW function (19) in the response, which the VLR GW function (19)stores in its memory.

After this the VLR GW function (19) forms a subscriber authenticationrequest and sends it to the SIP GW function (23). In the subscriberauthentication request is relayed a Random Number (RAND) and theciphering key sequence number. After receiving the subscriberauthentication request the SIP GW function (23) forms an INFO message tobe sent to the session control function (9) of the IP multimediasubsystem (101). Instead of the INFO message the SIP GW function (23)can create and send a corresponding unauthorized response to the sessioncontrol function to be relayed to the multi-radio protocol gateway (4)as was sent by the session control function (9) to the multi-radioprotocol gateway (4) to the first SIP registration request received fromthe multi-radio protocol gateway (4). However, in this example INFOmessages are used.

In the request URI of the INFO message the SIP GW function (23) sets thedomain name or the multi-radio protocol gateway or its numeric IPaddress. In the To header field the SIP GW function (23) sets the domainname of the same multi-radio protocol gateway (4) or its numeric IPaddress. In the From header field the SIP GW function (23) in turn setsthe domain name of the register gateway (24) or its numeric IP address.In addition, the INFO message includes a message body for sessiondescription, to which the SIP GW function (23) connects the data fromthe subscriber authentication request: the random number and theciphering key sequence number.

As the type of the message body for description is specified anapplication and as the name for example MRGW. These are set in theContent-Type header field. The data from the subscriber authenticationrequest are relayed each in their own parameter, for example in thefollowing manner: OperationCode=authentication request,InvokelD=subscriber identity, RAND=random number and CKSN=ciphering keysequence number. Alternatively the SIP GW function (23) could relay theentire subscriber authentication message received from the VLR GWfunction (19) as such in the message body for description of the INFOmessage.

The SIP GW function (23) sends the INFO message to the session controlfunction (9) of the IP multimedia subsystem (101) via the interface ISC(72). The session control function (9) relays the INFO message to themulti-radio protocol gateway (4). After receiving the INFO message theSIP GW function (20) of the multi-radio protocol gateway first sends anOK response to the session control function (9) and then forms theoriginal subscriber authentication request from the parameters of themessage body for description of the INFO message and relays it to theSGW function (22), which relays it further to the terminal (6) via theinterface A (50), IuCS (71) or Up (52). The terminal (6) responds to thesubscriber authentication request with an authentication response, whichincludes a Signed Response (SRES).

After receiving the authentication response the SGW function (22) relaysit further to the SIP GW function (20), which forms an INFO message fromit. In the request URI of the INFO message the SIP GW function (20) setsthe domain name or the register gateway (24) or its numeric IP address.In the To header field the SIP GW function (20) sets the domain name ofthe same register gateway (24) or its numeric IP address. In the Fromheader field the SIP GW function (20) in turn sets the domain name ofthe multi-radio protocol gateway (4) or its numeric IP address. In theContent-Type header field the SIP GW function (20) sets application asthe type of the message body for description and RGW as the applicationname.

As the parameters of the message body for description the SIP GWfunction (20) sets OperationCode=authentication response,InvokelD=subscriber identity and SRES=identity response. The SIP GWfunction (20) sends the INFO message to the session control function (9)of the IP multimedia subsystem (101) via the interface Gm (61).

After receiving the INFO message the session control function (9) sendsit to the SIP GW function (23) of the register gateway (24). Afterreceiving the INFO message the SIP GW function (23) of the registeringgateway (24) first responds with an OK response to the session controlfunction (9) and after this forms the original authentication responsefrom the received INFO message and relays it further to the VLR GWfunction (19). After receiving the authentication response the VLR GWfunction (19) compares the received identity response to thecorresponding stored response and when they match, the user has beenauthenticated acceptably.

When the user has been authenticated acceptably, the VLR GW function(19) sends a location updating request to the home location register (7)of the user via the interface D (75). The home location register (7) ofthe user responds by sending to the VLR GW function (19) the subscriberdata related the circuit-switched services etc. of the public mobilephone system, which the VLR GW function (19) saves in its database (or acorresponding memory). After the home location register (7) has acceptedthe location updating, if the re-allocation of the temporary subscriberidentity must be performed, the VLR GW function (19) forms a cipheringmode setting request and relays it to the SIP GW function (23).

In the ciphering mode setting request is relayed the ciphering mode andthe ciphering key to be used. After receiving the ciphering mode settingrequest the SIP GW function (23) forms an INFO message of it to be sentto the session control function (9) of the IP multimedia subsystem(101). In the request URI of the INFO message the SIP GW function (23)in turn sets the domain name of the multi-radio protocol gateway (4) orits numeric IP address. In the To header field the SIP GW function (23)sets the domain name of the same multi-radio protocol gateway (4) or itsnumeric IP address. In the From header field the SIP GW function (23)sets the domain name of the register gateway (24) or its numeric IPaddress. In the Content-Type

header field of the INFO message an application is specified as the typeof the message body for description and for example MRGW as the name ofthe application.

The ciphering mode received in the ciphering mode setting request isrelayed with the parameter of the message body for description of theINFO message, for example, in the following manner:OperationCode=ciphering mode setting request, InvokelD=subscriberidentity, Ciphering Mode=ciphering mode and Kc=ciphering key. The SIP GWfunction (23) sends the INFO message to the session control function (9)of the IP multimedia subsystem (101) via the interface ISC (72). Afterreceiving the INFO message the session control function (9) relays it tothe SIP GW function (20) of the multi-radio protocol gateway (4). Afterreceiving the INFO message the SIP GW function (20) of the multi-radioprotocol gateway (4) first sends an OK response to the session controlfunction (9) and then forms the original ciphering mode setting requestfrom the parameters of the message body for description of the receivedINFO message and relays it further to the SGW function (22), whichrelays it further to the wireless access network (104) via the interfaceA (50), IuCS (71) or Up (72). After the ciphering code setting the VLRGW function (19) of the register gateway (24) activates theInternational Mobile Equipment Identity (IMEI) of the terminal (6) byrelaying an identity request to the SIP GW function (23) where it statesthe requested identity type, which in this case is, therefore, theinternational mobile equipment identity.

After receiving the identity request the SIP GW function (23) forms anINFO message of it, as described above, to be sent to the sessioncontrol function (9) of the IP multimedia subsystem (101) via theinterface ISC (72). In the Content-Type header field of the INFO messagean application is specified as the type of the message body fordescription and, for example, MRGW as the name of the application. Theidentity type received in the identity request is relayed with theparameter of the message body for description of the INFO message forexample in the following manner: OperationCode=identity request,InvokelD=subscriber identity and MobileldentityType=identity type.

The SIP GW function (23) sends the INFO message to the session controlfunction (9) of the IP multimedia subsystem (101) via the interface ISC(72). After receiving the INFO message the session control function (9)sends it to the SIP GW function (20) of the multi-radio protocol gateway(4). After receiving the INFO message the SIP GW function (20) of themulti-radio protocol gateway (4) first sends an OK response to thesession control function (9) and then forms the original identityrequest from the parameters of the message body for description of thereceived INFO message and relays it to the SGW function (22), whichrelays it further to the terminal (6) via the interface A (50), IuCS(71) or Up (52).

The terminal (6) responds to the identity request with an identityresponse, which includes the international equipment identity. Afterreceiving the identity response the SGW function (22) relays it furtherto the SIP GW function (20), which forms an INFO message from it. In therequest URI of the INFO message the SIP GW function (20) sets the domainname of the register gateway (24) or its numeric IP address. In the Toheader field the SIP GW function (20) sets the domain name of the sameregister gateway (24) or its numeric IP address. In the From headerfield the SIP GW function (20) in turn sets the domain name of themulti-radio protocol gateway (4) or its numeric IP address. In theContent-Type header field the SIP GW function (20) sets application asthe type of the message body for description and RGW as the applicationname. As the parameter of the message body for description the SIP GWfunction (20) sets OperationCode=identity response, InvokeID=subscriberidentity, MobileldentityType=identity type and IMEI=internationalequipment identity.

The SIP GW function (20) sends the INFO message to the session controlfunction (9) of the IP multimedia subsystem (101) via the interface Gm(61). After receiving the INFO message the session control function (9)sends it to the SIP GW function (23) of the register gateway (24). Afterreceiving the INFO message the SIP GW function (23) of the registergateway (24) first responds with an OK response to the session controlfunction (9) and after this forms the original identity response fromthe received INFO message and relays it further to the VLR GW function(19). After receiving the identity response the VLR GW function (19)requests the international equipment identity from the equipmentidentity register (8) via the interface F (77). The equipment identityregister (8) sends to the VLR GW function (19) the internationalequipment identity, which the VLR GW functions (19) compares to theequipment identity received from the terminal (6) and when they match,the VLR GW function relays the location updating acceptance response tothe SIP GW functions (23) including the new temporary subscriberidentity and the user's international mobile phone number.

After receiving the location updating acceptance response the SIP GWfunction (23) creates an OK response connected to the received SIPregistering request, which response includes the data from the messagebody for description of the location updating acceptance response. Asthe type of the message body for description is specified an applicationand for example MRGW as the name. These are set in the Content-Typeheader field. The data from the location updating acceptance response isrelayed each in their own parameter, for example in the followingmanner:

OperationCode=location updating acceptance response,

InvokelD=subscriber identity,

TMSI=new temporary subscriber identity; and

MSISDN=international mobile phone number.

The SIP GW function (23) sends the OK message to the session controlfunction (9) of the IP multimedia subsystem (101) via the interface ISC(72). The session control function (9) relays the OK response to themulti-radio protocol gateway (4). After this the VLR GW function (19)relays the location updating acceptance response to the DNS GW function(21). After receiving the location updating acceptance response the DNSGW function (21) can update in the domain name service (40) the SIPprocedure as the primary connection establishing procedure of the nameof the domain name service of the user's international mobile phonenumber (i.e. ‘SIP+E2U’) and as the address of the domain name serviceconnected to the SIP procedure (i.e. the domain name) the addressconnection from the Contact header field of the SIP registrationsrequest, for example, the user's international mobile phone number as acharacter string+‘:’ character+‘MSISDN’ character string+‘@’character+domain name of the multi-radio protocol gateway (4) or itsnumeric IP address, in the form of a SIP resource identity via theinterface Ddns (78).

As a secondary connection establishing procedure for the name of thedomain name service of the user's international mobile phone number theDNS GW function (21) can set, for example, a conventional phone callsetup procedure and as the address the user's international phone numberin the form of a resource locator meant for a phone number. If thedomain name of the user's international mobile phone number is not inthe domain name service (40), the DNS GW function (21) adds the domainname of the user's international mobile phone number and the otherspecifications to the domain name service (40). This data can beutilized, for example, in the ENUM service. It is to be noted that it isalso possible to update as the connection establishing procedure in thedomain name service (40) for example, ‘Skype+E2U’ and as a correspondingaddress a Skype identity. It is also to be noted that theabove-presented updating of the domain name service (40) can also beperformed by the session control function (9) of the IP multimediasubsystem (101) in connection with user registration via the interfaceDdns (78). Further, it is to be noted that the home subscriber server(11) can update in the domain name service (40) the SIP procedure as onesecondary connection establishing procedure for the name of the domainname service of the user's international mobile phone number, and theaddress connection addressing the session control function (9) as theaddress of the domain name service connected to the SIP procedure viathe interface Ddns (78) after receiving the notice related to userregistration from the session control function (9) according to the 3GPPrecommendations.

When the SIP GW function (20) of the multi-radio protocol gateway (4)receives the OK response from the session control function (9), theregistration to the IP multimedia subsystem (101) has succeeded. If theContact header field of the received OK response now also has some otheraddress connection than the above-mentioned registered addressconnection addressing the multi-radio protocol gateway (4) in question,which connection follows the resource identity structure according tothe SIP session procedure including the user's international mobilephone number as a character string+‘:’ character+‘MSISDN’ characterstring+‘@’ character+some domain name or a numeric IP address, i.e. theprevious registration to the IP multimedia subsystem (101) via someother multi-radio protocol gateway, that other address connection can beremoved by sending a registration request to the IP multimedia subsystem(101), the expiration time of which request is 0 seconds and the Contactheader field now has that other address connection.

When the multi-radio protocol gateway (4) receives the final OK responsefrom the session control function (9), the SIP GW function (20) sends alocation updating response indicating acceptance to the SGW function(22), which relays it to the terminal (6). If the SIP registration failsfor some reason, the SIP GW function (20) rejects the location updating,which the SGW function (22) signals between the terminal (6) and the SIPGW function (20).

In the following, the functions connected to phone callestablishing/cancellation are described more in detail.

When the SGW function (22) of the multi-radio protocol gateway of FIG. 1receives a phone call establishing request from the terminal (6) via theinterface A (50), IuCS (71) or Up (52), it relays the request further tothe SIP GW function (20). If registration to the IP multimedia subsystemhas not been done, the SIP GW function (20) now performs theregistration according to the SIP session procedure to the IP multimediasubsystem (101) via the interface Gm (61) as presented above in the partof the description of registration to the IP multimedia subsystem. Inthis case the SIP GW function (20) receives the international phonenumber of the user from the phone call establishing request receivedfrom the terminal (6). When the registration to the IP multimediasubsystem (101) has been successfully performed, the SIP GW function(20) forms a SIP session request (INVITE) to be sent to the sessioncontrol function (9) of the IP multimedia subsystem (101).

To the request URI of the SIP session request the SIP GW function (20)sets the phone number of the user to be reached in the form of aresource locator meant for telephone numbers. The phone number of theuser to be reached is received from the phone call setup requestreceived from the terminal (6). In the To header field the SIP GWfunction (20) sets the public identity of the user to be reached, i.e.the registration address, which is in the form of a resource locatormeant for telephone numbers and includes the phone number of the user tobe reached received in the phone call establishing request. In the Fromheader field the SIP GW function (20) sets the caller's phone number inthe form of an URL meant for telephone numbers, which phone number theSIP GW function (20) receives from the phone call establishing requestreceived from the terminal (6). In the Contact header field the SIP GWfunction (20) sets the address connection connected to the sessionservices of the caller's SIP end point, to which address the SIPrequests and request responses meant for the caller's public identityare to be sent and which it stored in connection with registration.

The SIP session request also includes the message body for session mediadescription. The media is described with a set of parameters, whichspecify, inter alia, the network type, the domain name of the caller'sSIP end point, the domain name of the used media gateway, the mediatype, the media relay protocol, and the media coding method. The domainname of the caller's SIP end point is the domain name of the multi-radioprotocol gateway (4) in question. The domain name of the media gateway(15) being used is received from the system configuration data. Themedia coding method is, in turn, received from the phone callestablishing request received from the terminal (6). The SIP GW function(20) sends session request to the session control function (9) of the IPmultimedia subsystem (101) via the interface Gm (61).

After receiving the SIP session request the session control function(20) first sends a temporary response to the SIP GW function, afterwhich it forms an SIP session between the IP multimedia subsystem (101)and the terminal (6) via the SIP GW (20) and SGW (22) functions of themulti-radio protocol gateway (4). It is to be noted that in this casebetween the IP multimedia subsystem (101) and the SIP GW function (20)of the multi-radio protocol gateway (4) the connection is in accordancewith the SIP session procedure and between the SIP GW function (20) andthe terminal (6) it is in accordance with the circuit-switched phonecall setup procedure. Via the interface A (50) and IuCS (71) the SGWfunction (22) relays over a circuit-switched connection when theterminal (6) uses a radio network of a public mobile phone system (i.e.a real circuit-switched connection) and via the interface Up (51) theSGW function (22) relays over a TCP/IP connection of a circuit-switchedconnection in accordance with the UMA specification when the terminal(6) uses an UMA connection. Cancellation of the connection takes placein a corresponding manner by signaling it between the IP multimediasubsystem (101) and the terminal (6) via the SIP GW (20) and SGW (22)functions of the multi-radio protocol gateway (4).

The phone call can also be established from the IP multimedia subsystem(101) to the terminal (6).

When the SIP GW function (20) of the multi-radio protocol gateway (4)receives an SIP session request from the session control function (9) ofthe IP multimedia subsystem (101) via the interface Gm (61), it convertsthe SIP session request into a circuit-switched phone call setup requestand relays it further to the SGW function (22). The phone numbers of theuser to be reached and the caller, which are necessary in the phone callsetup request relayed to the SGW function (22), the SIP GW function (20)now receives from the registration addresses of the To and From headerfields of the SIP session request. The SIP GW function (20) receives thephone number of the user to be reached from the request resourceidentifier as well. The phone call setup request must also include thecoding method of the media being used, which is received from thedescription message body of the media of the session request. Afterreceiving the phone call setup request the SGW function (22) firstperforms a paging procedure, with which the terminal (6) is made toreceive a phone call setup request, if the connection between theterminal (6) and the multi-radio protocol gateway (4) is not alreadyactive. When the terminal (6) has answered the page, the SGW function(22) relays the phone call setup request to the terminal (6), afterwhich the phone call setup is signaled between the terminal (6) and theIP multimedia subsystem (101) via the SGW (22) and SIP GW (20) functionsof the multi-radio protocol gateway (4). In the first session requestresponse, where the description message body of media is allowed, theSIP GW function (20) relays, in addition to the relay protocol andcoding method of the media being used, the domain name of the SIP endpoint of the user to be reached, as well as the domain name of the mediagateway (15) being used. The domain name of the SIP end point of theuser to be reached is the domain name of the multi-radio protocolgateway (4) in question. The domain name of the media gateway (15) beingused is received, for example, from the system configuration data.

The invention claimed is:
 1. A method comprising: connecting a terminalin an IP multimedia subsystem by sending a registration request to theIP multimedia subsystem, said request identifying the terminal by an SIPend point associated with a multi-radio protocol gateway instead of atelephone number; setting a private user identity for the terminal;setting a home network registrar domain name for the terminal;establishing a secure connection between the terminal and the IPmultimedia subsystem; setting, with an SIP gateway function stored onthe multi-radio protocol gateway, a private user identity for theterminal; setting, with an SIP gateway function stored on themulti-radio protocol gateway, a home network registrar domain name forthe terminal, wherein the home network registrar domain name compriseseither the domain name of the multi-radio protocol gateway or a numericIP address for the multi-radio protocol gateway; authenticating theterminal in the IP multimedia subsystem; sending a location updatingrequest corresponding to the new registration request to the homenetwork registrar; performing a domain name service update in connectionwith the registering of the terminal in the IP multimedia subsystem. 2.The method according to claim 1, wherein performing a domain nameservice update in connection with a registration procedure to the IPmultimedia subsystem includes performing a delayed registrationprocedure of the IP multimedia subsystem in connection with a telephonecall setup signal from the circuit switched portion of the public mobilecore system when the multi-radio protocol gateway receives said user'stelephone number in connection with said telephone call setup signal. 3.The method according to claim 2 wherein said step of performing adelayed registration procedure comprises a conventional phone call setupprocedure or a proprietary procedure.
 4. The method according to claim1, wherein the domain name service update includes sending the locationupdate request from the IP multimedia subsystem to a location registerpart of the public mobile phone via a serving gateway in a multi-radioprotocol gateway.
 5. The method according to claim 1, wherein settingthe private user identity comprises deriving the private user identityfrom the user's international mobile subscriber identity from itscountry and network codes.
 6. The method according to claim 1, whereinsetting the home registrar domain name comprises setting the homeregistrar domain name to the Request Uniform Resource Identifier of theregistration request.
 7. The method according to claim 1, furthercomprising sending from the IP multimedia system, via the secureconnection, an unauthorized response to the multi-radio protocol gatewayto start an authentication procedure.
 8. The method according to claim1, further comprising, prior to sending a new registration request tothe IP multimedia subsystem, the terminal comparing portions of theauthentication token to an authentication code received in a messagefrom the IP multimedia system.
 9. The method according to claim 1,wherein sending a location updating request to the home networkregistrar further comprises a gateway function receiving subscriber datafor the terminal.
 10. A method comprising: forming an integratedconnection between a multi-radio protocol gateway and an IP multimediasubsystem, setting, with an SIP gateway function stored on themulti-radio protocol gateway, a private user identity for a terminalconnected to the multi-radio protocol gateway; setting, with the SIPgateway function stored on the multi-radio protocol gateway, a homenetwork registrar domain name for the terminal, wherein the home networkregistrar domain name comprises either the domain name of themulti-radio protocol gateway or a numeric IP address for the multi-radioprotocol gateway; creating and maintaining a secure and encryptedconnection between the multi-radio protocol gateway and the IPmultimedia subsystem by implementing the SIP gateway function on themulti-radio protocol gateway to register the terminal in the IPmultimedia subsystem, wherein the multi-radio protocol gateway createssaid secure and encrypted connection to the IP multimedia subsystem andrelays, to the IP multimedia subsystem, the private user identity andthe home network registrar domain name as parameters of the terminal andwherein the multi-radio protocol gateway uses said parameters forcreating and maintaining said integrated connection to the IP multimediasubsystem.
 11. The method according to claim 10, wherein the parametersinclude a private user identity.
 12. The method according to claim 11,further comprising deriving the private user identity from the user'sinternational mobile subscriber identity from its country and networkcodes.
 13. The method according to claim 10, further comprising settingthe home registrar domain name to the Request Uniform ResourceIdentifier of an SIP registration request.
 14. The method according toclaim 10, wherein creating an integrated connection comprisesestablishing a secure connection between the terminal and the IPmultimedia subsystem.
 15. The method according to claim 10, whereincreating the integrated connection comprises authenticating the terminalin the IP multimedia subsystem.
 16. The method according to claim 10,wherein creating the integrated connection comprises sending a locationupdating request to a home network registrar.
 17. The method accordingto claim 10, wherein creating the integrated connection comprisesperforming a delayed registration procedure to the IP multimedia system.18. The method according to claim 10, wherein creating the integratedconnection comprises the multi-radio protocol gateway receiving atelephone call setup signal from a circuit switched portion of a publicmobile core system.